$]

The version + patchlevel / 1000 of the Perl interpreter. This variable
can be used to determine whether the Perl interpreter executing a
script is in the right range of versions. (Mnemonic: Is this version
of perl in the right bracket?) Example:

warn "No checksumming!\n" if $] < 3.019;

See also the documentation of use VERSION and require VERSION
for a convenient way to fail if the running Perl interpreter is too old.

The floating point representation can sometimes lead to inaccurate
numeric comparisons. See $^V for a more modern representation of
the Perl version that allows accurate string comparisons.